Get a list of all root-to-leaf paths in a DOM tree

Question

So far I understood that when I parse an XML as a DOM object it is represented as a tree. I'm trying to get a list of all the paths from root to any leaf of my XML document (n-ary tree) with the TreeWalker, however I'm wondering if I should do my own implementation or there's any existing implementation defined. I found none in the official documentation.

Given the xml document:

<node id="A">
   <node id = "AA">
       <node id = "AAA"></node>
   </node>
   <node id = "AB">
   </node>
   <node id = "AC">
   </node>
</node>

The expected list should contain:

A, AA, AAA 
A, AB
A, AC

Answer 1

i would use some algorithm like this:

go down in tree with one function and if you have no child, go up and output every parent node.

 function deep(node n){
    if(n has childs)
       foreach(child c) {
          deep(c);
       }
    else goup(n);
 }

 function goup(node n){
     if(node has no parent) echo n.id
     else echo goup(n.parent()) . ", " . n.id
 }

Answer 2

Non-recursive TreeWalker

It's fairly simple. Find all leaf elements, then display path by walking the parent chain.

NodeFilter leafElements = new NodeFilter() {
    @Override
    public short acceptNode(Node node) {
        for (Node child = node.getFirstChild(); child != null; child = child.getNextSibling())
            if (child.getNodeType() == Node.ELEMENT_NODE)
                return NodeFilter.FILTER_SKIP;
        return NodeFilter.FILTER_ACCEPT;
    }
};
TreeWalker walker = ((DocumentTraversal)document).createTreeWalker(document.getDocumentElement(),
                                                                   NodeFilter.SHOW_ELEMENT,
                                                                   leafElements,
                                                                   false);
for (Element leaf; (leaf = (Element)walker.nextNode()) != null; ) {
    Deque<String> path = new ArrayDeque<>();
    for (Node node = leaf; node.getNodeType() == Node.ELEMENT_NODE; node = node.getParentNode())
        path.addFirst(((Element)node).getAttribute("id"));
    System.out.println(path);
}

Output

[A, AA, AAA]
[A, AB]
[A, AC]

---

Simple Recursion

Also fairly simple. Recurse descendants, maintaining path so far, and print for leaf elements.

showLeafPaths(document.getDocumentElement(), new StringBuilder());

private static void showLeafPaths(Element elem, StringBuilder path) {
    final int pathLen = path.length();
    if (pathLen != 0)
        path.append(", ");
    path.append(elem.getAttribute("id"));
    boolean hasChild = false;
    for (Node child = elem.getFirstChild(); child != null; child = child.getNextSibling())
        if (child.getNodeType() == Node.ELEMENT_NODE) {
            hasChild = true;
            showLeafPaths((Element)child, path);
        }
    if (! hasChild)
        System.out.println(path);
    path.setLength(pathLen);
}

Output

A, AA, AAA
A, AB
A, AC